1. Field of the Invention
The present invention generally relates to an enclosure that provides physical protection and storage for cables such as those used in telecommunications, and more particularly to an above-ground closure for optical fibers, splices and connectors therefor, the closure having hinged, fiber optic storage trays and fiber breakout tubes guiding fibers from one tray to another.
2. Description of the Prior Art
It is frequently necessary to join the ends of two cables, such as are used in telecommunications, to lengthen the cable system, branch off additional cables, or repair damaged cables. It is common to use enclosures to protect the joints, whether aerial, direct buried, above-ground or below ground (plant or hand hole). The enclosures are generally one of two types, in-line or butt-splice. In the butt splicing of fiber optic cables, several enclosure designs employ a dome shape, i.e., a closure body that is generally elongate, and has a closed end and an open end. Several such designs are depicted in U.S. Pat. Nos. 4,927,227, 5,222,183, 5,249,253 and 5,278,933, and in PCT Application No. GB93/00157.
These closures use various clamps, bolts, ties, etc., to secure the cable near the open end of the closure. See U.S. Pat. Nos. 5,097,529, 5,280,556 and 5,288,946, and PCT Application Nos. US93/05742, GB93/01120 and GB93/01942. These elements provide strain relief against cable stresses caused by external cable movement relative to the closure. A cable that is pulled or pushed axially, twisted, or bent must not transmit that motion to the cable sheath opening inside of the closure. The prior art designs are less suited for fiber optic cables, however, since they include metallic components have sharp edges which can damage exposed fibers and their coatings. These designs also require many parts, increasing the cost of the closure, and sometimes require special tools for installation. The use of so many interconnecting parts additionally increases installation time.
Some prior art cable terminations use shield bond connectors to additionally secure the cable jacket, and to provide electrical continuity across grounding sheaths, using metallic braids. These connectors typically have an inner clamping member which fits inside the cable jacket, and an outer clamping member which grips the outer surface of the cable jacket, and a bolt or other means for forcing the two members together to clamp the jacket therebetween. See, e.g., U.S. Pat. Nos. 3,787,797, 4,895,525 and 5,097,529, PCT Application No. US94/04198 and German Patent No. 4,231,181. These designs are inadequate to rejoin the integrity of the cable jacket for both fiber optic and copper cables since, for example, they cannot adequately handle the strength members found in fiber optic cables, such as wires or aramid fibers. Indeed, it would be very useful to have a connector that allowed for easier conversion from copper shield bond to fiber shield bond.
In several of the foregoing designs, fiber optic storage trays, such as splice trays, are supported by or attached to the strain relief member or closure body. The storage trays usually include guide walls to maintain the fibers with a minimum bend radius. In the aforementioned '227, '183, and '253 patents, and in U.S. Pat. Nos. 5,323,480 and 5,363,466, several splice trays, stacked during storage, are hinged to a common base, in a stair-step fashion. U.S. Pat. No. 5,071,220 and PCT Application No. US94/04232 show in-line closures having trays hinged to a common base in this manner. In U.S. Pat. No. 5,323,478, the trays are stacked by means of hinging strips. These hinging arrangements still allow the fibers traveling between adjacent splice trays to become kinked when the tray is lifted, inducing microbend losses in the fiber. They also do not make the best use of space due to the stair-step geometry.
Fibers that are routed between trays are often protected in spiral wrap tubing or cylindrical tubing to keep the fibers from being physically damaged and to resist bending of the fiber to less than its minimum bend radius. Cylindrical tubing and spiral wrap both take a fair amount of time to install since, for cylindrical tubing, the fibers must be threaded through the tubing and, for spiral wrap, the wrap must be hand coiled about the fibers, which can be very difficult if a long length of fiber is present. With spiral wrap, it is also easy to pinch a fiber as it is wrapped. Prior art fiber breakout tubes further do nothing to keep ribbon fiber from unduly twisting.
Several of the splice trays shown in the aforementioned patents use splice cradles which retain a plurality of splice elements. See also U.S. Pat. Nos. 4,793,681, 4,840,449 and 4,854,661. The retention features can be molded directly into the tray surface, as disclosed in U.S. Pat. No. 5,074,635. Splice inserts can be removably attached to the trays, having retention features in the form of flexible cantilever latches for a snap fit; see U.S. Pat. Nos. 4,489,830, 4,679,896 and 5,375,185. These latches do not always firmly grip the splice elements, if many elements are present in adjacent grooves, due to the displacement and tolerance build-up of the material forming the retention feature. Repeated or extended use of the splice inserts can also lead to weakening of the retention members. In light of all of these problems, and particularly those associated with closures for fiber optic cables, it would be desirable and advantageous to devise a fiber optic closure having appropriate components to overcome the foregoing limitations.